Signalling and Safety at Sea. 5 



Automatic bell-buoys are common around our coasts at the 

 present time ; and buoys which show an occulting light are 

 ■also common. Very often both functions are performed by 

 the one buoy. .The bell-stroke is operated by energy derived 

 from the motion of the waves. There is, even under 

 conditions of apparent calm, considerable energy available 

 from this source. It is not necessary for the bell to be 

 struck at regular intervals, but it is of importance that the 

 blow upon the bell should always be given with the same 

 force, so that the sound emitted should be of uniform 

 loudness. We may suppose, then, that the up and down 

 movements of the buoy, however gentle and slow, are 

 resisted by a horizontal vane immersed in the water beneath. 

 This vane, as it oscillates respecting the buoy with the rise 

 and fall of the latter, compresses, by means of a ratchet, a 

 spring which when stressed to a certain degree is released 

 and its stored energy expended in actuating the hammer. 

 As we shall see later very similar mechanism is in frequent 

 and successful use. We have, then, a bell-stroke in air, at 

 intervals, and made with a certain constant force. It is 

 matter of observation that even in calm weather three or 

 more strokes will be given per minute. We would require, 

 in fact, a certain controlling mechanism limiting the number 

 of strokes to, say, 3 per minute. 



I assume now that a light-flashing system is also installed 

 upon this buoy similar to many of the blinking or occulting 

 lights marking sand-bank or other danger close to the shore. 

 A connexion between the mechanism actuating the hammer 

 and that causing the occultation of the light is arranged, of 

 such a nature that simultaneously with the stroke of the bell 

 there is a sudden flare-up of the light, or sudden luminous 

 flash, followed by a succession of flashes spaced at short 

 regulated intervals. 



We can so order the signals that the sailor making 

 harbour requires no stop-watch to measure the lag of the 

 sound upon the light signal. The light flashes, repeated at 

 regular intervals, themselves afford the measure of the lag of 

 the sound waves. For suppose 20 successive light flashes 

 spaced at such an interval of time as the sound takes to travel 

 one-tenth of a nautical mile — that is one cable. .Flashes so 

 timed are easily counted, this interval (0""53) being very 

 little over one-half second. Then if the first flash is emitted 

 0'53 second later than the instant of the first bell-stroke, 

 when the first flash reaches the ship the sound has already 

 travelled one cable, and if the sailor is at the distance of 

 one cable he hears the stroke of the bell at the instant at 



